watertight and sufficiently large to permit a free
flow of concrete. Keep the discharge end
continuously submerged in fresh concrete. Keep the
shaft full of concrete to a level well above the
water surface. Discharge and spread the concrete by
raising the tremie to maintain a uniform flow.
Place concrete without interruption until the top of
the fresh concrete is at the required height."
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Place concrete as soon as practicable after the forms and the
reinforcement have been inspected and approved. Do not place concrete when
weather conditions prevent proper placement and consolidation; in uncovered
areas during periods of precipitation; or in standing water. Prior to
placing concrete, remove dirt, construction debris, water, snow, and ice
from within the forms. Deposit concrete as close as practicable to the
final position in the forms. Do not exceed a free vertical drop of one m 3
feet from the point of discharge. Place concrete in one continuous
operation from one end of the structure towards the other or lifts for
vertical construction. Position grade stakes on 3 m 10 foot centers
maximum in each direction when pouring interior slabs and on 6 m 20 foot
centers maximum for exterior slabs.
3.4.1
Vibration
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NOTE: The requirement for vibrator spacing shall be
considered in the reinforcing steel design by the
engineer of record. ACI SP-66 requires that bar
bundling be done by the design engineer. It is very
important to provide space for placement and
consolidation of concrete.
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Comply with the requirements of ACI 309R and ASTM A 934/A 934M using
vibrators with a minimum frequency of 9000 vibrations per minute (VPM).
Use only high cycle or high frequency vibrators. Motor-in-head 60 cycle
vibrators may not be used. For walls and deep beams, use a minimum of two
vibrators with the first to melt down the mixture and the second to
thoroughly consolidate the mass. Provide a spare vibrator at the casting
site whenever concrete is placed. Place concrete in 500 mm 18 inch maximum
vertical lifts. Insert and withdraw vibrators approximately 500 mm 18
inches apart. Penetrate at least 200 mm 8 inches into the previously
placed lift with the vibrator when more than one lift is required. Extract
the vibrator using a series of up and down motions to drive the trapped air
out of the concrete and from between the concrete and the forms.
For slab construction use vibrating screeds designed to consolidate the
full depth of the concrete. Where beams and slabs intersect, use an
internal vibrator to consolidate the beam. Do not vibrate concrete placed
with anti-washout admixtures. Vibrators shall be equipped with rubber
vibrator heads.
[3.4.2
Application of Epoxy Bonding Compound
Apply a thin coat of compound to dry, clean surfaces. Scrub compound into
the surface with a stiff-bristle brush. Place concrete while compound is
tacky. Do not permit compound to harden prior to concrete placement.
Follow manufacturer's instructions regarding safety and health precautions
SECTION 03311
Page 34
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